User:Jtwsaddress42/Gallery/Romer, Alfred Sherwood - The Functional Welding of the CNS to the ENS

The Functional Welding of the CNS to the ENS - The Autonomic Nervous System "To sum up the phylogenetic suggestions gained from a consideration of the structure of the nervous system in living vertebrates, high and low, and of their chordate and protochordate "ancestors," one tends strongly to gain the impression that the remote "visceral" ancestral form had a simple superficial nerve net and, at some early stage, acquired a visceral nerve net as well; that, with the development of the "somatic" animal, there developed the central nervous system, with segmental nerves including a ventral root of somatic motor type and a distinct dorsal root at first composed merely of somatic sensory neurons; but that there was a strong tendency for the somatic animal to attempt neural control over the visceral animal, first perhaps, by a direct connection with the important visceral muscles of the pharynx, later by an attempt to dominate the gut by autonomic fibers, originally by way of dorsal nerve roots, running to the postganglionic neurons, which represent elements of the original gut nerve net. The development of visceral centers in brain and cord was associated with this attempt at domination of the visceral by the somatic animal. But, as we are ourselves aware, the integration of the visceral animal into the dominant nervous system of our somatic being is still far from perfect." Alfred Sherwood Romer (1972) Romer, Alfred Sherwood (1972). The Vertebrate as a Dual Animal — Somatic and Visceral.". In Dobzhansky T., Hecht MK, and Steere WC. . Evolutionary Biology (New York, NY: Springer): 121–156. doi:10.1007/978-1-4684-9063-3_5. ISBN 978-1-4684-9065-7. https://link.springer.com/chapter/10.1007%2F978-1-4684-9063-3_5.

The Functional Welding of the CNS to the ENS. The points of fusion between larval and adult bodyplans - Unmyelinated parasympathetic system. Tunicate adult bodyplan - Pharyngeal arch system with visceral enteric nervous system (ENS). Tunicate larval bodyplan - Somatic CNS, head senses, notochord, segmented musculature, and post anal tail. Gaining control - Myelinated sympathetic system exerting control by the somatic CNS over the visceral ENS.

The Functional Welding of the CNS to the ENS - Gaining Control "It is not unreasonable to speculate on the possibility that: The ancestor of the vertebrates may have had, like many invertebrate types, an essentially independent visceral nerve net; that the development of the autonomic system represents an attempt by the central nervous system at gaining control over visceral activity; and that possibly in the peculiar two-neuron system seen here, the post-ganglionic neurons may be representatives of the original visceral nerve net system, the pre-ganglionics representatives of attempts at domination by the central nervous system." Alfred Sherwood Romer (1972) Romer, Alfred Sherwood (1972). The Vertebrate as a Dual Animal — Somatic and Visceral.". In Dobzhansky T., Hecht MK, and Steere WC. . Evolutionary Biology (New York, NY: Springer): 121–156. doi:10.1007/978-1-4684-9063-3_5. ISBN 978-1-4684-9065-7. https://link.springer.com/chapter/10.1007%2F978-1-4684-9063-3_5.